Abstract: A low capital cost, energy efficient process for separation of carbon dioxide, sulfide gases and hydrocarbons from carbonaceous off-gas streams, for example, oil shale retorting off-gases, coal gasification off-gases, oxygen fire flooding off-gases or carbon dioxide miscible flood enhanced oil recovery off-gases is disclosed. The process comprises separation of the off-gases into an essentially sulfur-free light fuel gas, a heavy hydrocarbon stream and a carbon dioxide gas stream wherein the off-gas is compressed if necessary and cooled prior to separation of the various streams in a distillation column. The carbon dioxide stream is expanded in an auto-refrigeration step to provide some of the necessary process refrigeration.

Abstract: A process is described for separating a carbonaceous off-gas in a low temperature distillative separation to produce a fuel gas stream, a carbon dioxide-sulfur stream and a heavy hydrocarbon stream wherein the carbon dioxide-sulfur stream is reduced in pressure to produce refrigeration to return a portion of the fuel gas stream as reflux to the distillation, and the fuel gas stream, now at relatively higher pressure than the carbon dioxide-sulfur stream, is passed over a semi-permeable membrane selective to carbon dioxide to separate carbon dioxide from the fuel gas to combine the permeate carbon dioxide with the carbon dioxide-sulfur stream.